If you are a regular and HVC Chase customer and do not regularly initiate questionable chargebacks, Chase will typically simply grant smallish chargebacks such as that and not bother with the process or the restaurant may have advised its merchant processor that it won't bother responding to smallish disputes. Just not worth the hassle.

In that case, you've got what amounts to a one-time pass for the whole thing which is more than you deserved, but it all comes down to the system working easier and faster.

If this was a restaurant with a business clientele it was most likely an input error as it's hard for people to put through receipts with tips like that.