There's a difference, might be a subtle difference but it makes all the difference.
Let's start by defining the two: A community is a feeling of fellowship with others, as a result of sharing common attitudes, interests and goals. While a fandom is the fans of a particular person, team, fictional series, etc. I'm sure most people don't see any difference and I can understand that to a certain extent, but hopefully I'll explain it well enough to make my point.
The biggest difference between the two is how people within these two things behave, to each other and those outside it. These behaviors hinge on the mentality of the commonalty. Since a community shares attitudes, interests and goals the overall mentality is almost always positive, with differences between members more often than not met with discussion and compromise or at the very least agreeing to disagree. After all they can't be that bad, they're all here for the same reason.
Meanwhile a fandom is all about enthusiasm for something or someone. Not inherently a bad thing, until that enthusiasm results in hostility towards those that are critical of the thing they're a fan off. As a fandom grows this hostility, while mostly harmless individually, compounds when a group gangs up on the person/s that have the gall to speak unfavorably of the thing they like. This hostility if left not moderated will fester and create a toxic environment for those that would like to participate in the discussions around something that aren't implicitly praising the thing.
Why do I bring all this up? Well, Rooster Teeth has less of a community and more of a fandom these days, they still call it a community and there's some truth in that still but it's approaching a precipice where hostility will take hold and never let go. It's always happening in YouTube comments because that's what YouTube comments are, but hints of it are happening on this site. The people who signed up for this site like RT and/or AH and should be viewed as part of the same group as everyone else... but it's starting to happen, negative comments and thumbs down directed at other members is becoming common, especially when it deals with criticism of RT.
Yes, I'm talking about the rape jokes in the finale of On The Spot. More specifically the people who were offended by them that took the time to comment their disappointment in them. They are getting a considerable number of thumbs down while comments telling those that are offended, that they shouldn't be offended, are getting thumbs up. This isn't something a healthy community does, this is a symptom of RTs community losing it's fellowship and becoming a typical unaccommodating and hostile fandom. If left unchecked eventually calling yourself a Rooster Teeth fan won't have a positive connotation to the rest of the world anymore. Maybe it won't get that bad but... it's certainly possible which is an outcome I wouldn't have dreamed possible a few years ago.
BTW, my opinion on rape jokes, they aren't funny. But if you want to make them and/or you laugh at them, that's fine. Just means you lack a certain context. But failing to understand or empathize with someone that might find them distasteful is a whole other issue, a much bigger issue. Statistically with the size of this site, a fair number of members have been sexually abused, and that's not funny and not caring about those unfortunate souls feelings is more than a little disheartening and shame on you.