I would make sure your saddle height is correct and you are not hyper extending your knee, usually people's saddles are too high. Next you can examine your pedal stroke, in that is your legs/knees are not flaring outward because that 100% can cause unneeded stress. Look into your Q-Factor, more than likely the newer bike is narrower in Q-Factor. Lastly, you could have just done too much too soon. If you said it was a "hard" ride and a lot of it was out of the saddle or you really gunning it yeah you might have just tweaked something. Naproxen or ibuprofen, rest, and ice if needed. Try light stretching or even a light bike ride the next couple rides out.

A couple weeks ago I tweaked a tendon on a ride I have done a thousand times, it's just on that ride I got a little extra and was pounding it on the climbs. I followed the ride up just with Naxproxen, keeping my following rides chill with little to no elevation, and just not pushing it at all. This weekend my leg felt great and I did a metric century.