It was probably an issue with that particular merchants POS. Merchants have very little incentive to update their POS systems so technology changes are very hard to get rolled out. Especially for smaller merchants which many restaurants are.

It’s a network effect thing. Because tap to pay wasn’t supported by the POS vendors US consumers did not get much improvement in experience because of it, so there wasn’t demand from merchants. With Apple Pay there is a huge improvement for consumers (not having to carry the credit card) it has finally forced merchants and their supporting POS vendors to support it.

Between that and the disruption in the POS market the iPad (and similar devices) brought, POS vendors have had to become more flexible.