Unfortunately, it is not possible to detect whether there is a grill or not with the paper adherence on the back. It needs to be soaked off before any checking can be done. The cancel is a common target, so doesn't help determine if cancelled later than the 1869 grilled issue.
I'm hardly an expert on the series, but to me that paper/impression doesn't look correct for the reissue vs. original, but that could be the scans.
It just looks (to me) like a normal 1869 stamp, but either the grill wasn't fully struck and got pressed out over time, or high-res scanning, watermarking, or other examination may ultimately reveal traces of the grill.