It seems to me that your proposed statement isn't yet out of the question. I interpreted this statement as basically saying "Don't worry, we've got real people on this, but we've not resolved anything yet." To me, that's better than them waiting for days or weeks with no acknowledgement, then issuing a complete statement like you recommended.
You bring up an important point, which is the speed with which they've addressed the issue. That deserves commendation, and is a very smart move on their part. It nips the story in the bud, which is important.
That said, this does not read as a preliminary post. It's titled, "Regretsy Issue Resolution". It makes no promises of further updates, and just says that they're dealing with the issue privately. That's their right, but I think it's a PR mistake. There are two issues in this case: 1) regretsy being treated as a scammer, and 2) the behavior and tone of the paypal representative. This post addressed 1 but not 2, and it doesn't look like there will be a second. This is a missed opportunity on paypal's part to turn the incident into a PR win.
