There’s no catch, just competition. Customers who currently pay for 25 megabit per second service will get 50 mbps; customers who pay for 50 will get 105, and customers who pay for 105 will get 150.
The Kansas City Star does point out that similar speed boosts have been put in place in other markets where Comcast does business, including in Texas, in California, and in the Northeast. Yet the choice of Kansas City surely has nothing whatsoever to do with the presence of Google Fiber in that area. Neither does AT&T’s build-out of their own gigabit fiber network.