OP YWBVU but I imagine your clear on that now. They were very rude, but a lack of pool etiquette will lead to incidents of 'lane rage'. There are a few things you would benefit from understanding if you intend becoming a regular swimmer - and I hope you do keep it up, it's a wonderful form of exercise.
Check the pace of the lanes before you get in, one day the medium lane may be full of slow swimmers and the fast lane maybe more appropriate, the next morning the medium lane may be full of triathletes and you are better suited to the slow lane.
Never, ever do anything other than fast crawl in the fast lane. They are usually the narrowest lane because it's expected people will be doing crawl, don't ever attempt breaststroke/backstroke/general fannying about - unless you are Olympic pace and the only person doing overtaking will be you.
Be prepared to switch lanes if the pace of the lane changes during your swim, I'm usually a fast lane swimmer but if faster swimmers get in during my session I will duck into the medium lane so as not to hold people up.
Be aware of people trying to overtake, move to the side at the end of a length and let them pass, or if they are much faster and want to pass mid lane, slow down, move right over and let them pass.
Don't ever push off and start a length in front of a faster swimmer, it's hard work overtaking people in a busy lane and they will be cursing you in their head.
If you are having a rest, move right to the edge of the lane so people can still turn and push off without kicking you in the crotch. Embarrassment for both parties.
If you want to do exercises, pick the slowest lane possible and avoid getting in the way of lane swimmers. Or ideally go out of lane swimming sessions, our pool has some women only sessions which are generally more tolerant/slower/less intimidating. Yours may have similar which you may enjoy whilst you get into the swing of things. Good luck!