The white part of the eyes being red is an indication of stress. Stress could be the excitement of the weekend - the car trip, visiting at your Mom's and that he's just worn out now. Could be he was somewhat allergic to the cat or maybe even helped himself to some litterbox treats (I know yuck!) and tummy might be upset. It can also be a sign of illness. Don't panic over the last comment.
How is he otherwise? - appetite okay? playful? energy level normal? If he is otherwise normal, maybe just napping a little more, then I'd suspect he's just had a very big weekend for a little puppy.
You're not being paranoid, but do get a bouquet of flowers for being a very observant Mom.
Just keep an eye on him and he begins acting off, then a vet visit might be in order.
Debbie