Puncture Repair Foam?!?

Just got new front tyres fitted today Goodyear F1 GSD3's. A bit slippy at first but after a few miles they are definitely the business. Loads of grip and the car feels a bit more nimble than before.

Anyway, to the point...the guy at the garage asked me if I'd ever had puncture repair foam sprayed into my wheels. I've never heard of the stuff but he said both fronts previously had this and that it can corrode the alloys. Is this something that Audi do? He said that the tyre pressure may start to drop if the rims get too corroded. Sounds a bit dangerous to me.

See, I bought the car from an Audi dealer with 6000 mls on it. I noticed that one of the fronts was a PZero and the rest were Pilot Sports so I figured there had been a puncture at some point and the PZero was the replacement.

The guy at the garage this morning said some places had been using the foam as a preventative measure in case of a puncture. In any case, both of mine were filled with it and I'm now thinking the rears may also have it but the only way to find out is to take them off. Not sure how much of the stuff was inside.