I think it's super neat. The barrel looks like an old rifle bolt.
I'm fairly certain is is, without seeing different angles to get a real bead on it. The slots in the lugs look ground in. I'm kind of betting the barrel is two pieces--either front and back pressed and/or soldered together and then cleaned up, or bored out and lined. An old BP cartridge if they barrel was scavenged from the same gun. If not, all bets are off.
This is definitely not a production piece. Fairly well designed for a garage job, at least. I'm pretty sure the spring guides are brazed on. I'd be surprised if the main portion of the body wasn't repurposed and cut from something else, probably considerably larger. Judging by that style of trigger, maybe an oiler or an early drill.
The checkering on the striker block says that either someone has a good hand with a file and a 'good enough' mentality or they tilted it 45 degrees in a vice to catch the edge of a cutting tool. Definitely a file on the... dongle? on the back.
Certainly the same person, or at least tool, that knurled the front of the barrel didn't do the rest. It's a lot harder to checker flat than knurl round.
Definitely ingenuity here, and either patience but little skill or vice versa.
Whatever it be, don't shoot it. If it's built like it looks, I wouldn't trust it to hold up to firing pressure for long. At best, your wrist would regret it. Assuming you can hang onto it.