I don't think it's a crack but just bad welding because I see a pinhole on the nondriveside stay and even the beads connecting the stays to the BB shell are just inconsistent compared to the seat tube to bb. The toes of the weld on the driveside stay appear to be cold and not enough amperage was given. The spot of concern I'm not sure is a crack but could be excessive filler or where got the tungsten stuck to the bead while welding. I'd worry more about the toe of the welds just below that "cracked" section. But overall I've seen worse looks to be just a asian built production welded frame. If it was supposed to be a high quality frame that cost some coin from a well known company then I'd complain. That's just my .02 from a TIG welder.