The cyclocross riders may well have been using this ride as a recovery ride. A recovery ride is where you don't raise your heartrate out of the comfort zone and you are riding to keep the muscles loose and ready to go.
It can be a lot of fun to ride in a group and motivating to see men and women in their 50's, 60's, and 70's not only riding but riding well enough to leave you behind.
Be sure to ask lots of questions about group etiquette and what is expected behavior. I didn't go on a group ride for a long time because I was afraid I'd cause a crash or something.
You will enjoy the rides more if you wear proper cycling clothes. Jeans are the worst things to wear as they bind in the crotch and knees and don't wick moisture. Cotton is another no-no fabric. If you can't bring yourself to wear spandex shorts, check out some mountain bike shorts, aka baggies. Now that you've gotten the bug, you'll naturally want to ride longer and harder rides and that's when the cycling clothes will really, really be a blessing.