I do not believe that incidental contact on this play is in the spirit of the rules, whether it is covered directly or not.

Now, a runner and fielder trying to field a ball collide and the fielder falls on the runner preventing him advancing, different story. But a fielder going to catch a ball knocks a guy off of the bag then tags him?

Calling an out is just lazy umpiring. You are looking to go home early, and I hope you are never my partner.