It could be. Or celery. Does it smell of celery when you tear a leaf? Whichever it is it has bolted so no longer useable except as a bit of greenery in cooking.

It also could be Lavage - perennial herb with celery aroma and same type of leaves. Never tried to use it same way as celery for fresh eating, but I use it for canning and cooking.

i bought the celeriac seeds from europe. i don't remember if i planted this one there. but it wasn't the usual vegetable planing area, i don't think that how it can land there from the sky. no one else was planing similar vegetable around.

so i am guessing maybe the european seller sent me the fake celeriac. it didn't seem to have a big root under the soil.

Just because it didn't bulb up doesn't mean it isn't Celeriac. Celeriac is actually quite difficult to grow successfully. I have failed plenty of times to get good big roots. The plant you have looks very much like Celeriac, or Celery, which has prematurely bolted. I don't see any reason to doubt the seller.

As to why it is there, a single seed could easily have got misplaced, maybe stuck to a sleeve or shoe, and got transferred to some other area of the garden. I am sure Celeriac seed it readily available in the States if you want to try again.

BTW I don't think it is Lovage. The leaves aren't right. Lovage has less heavily toothed and smoother leaves. Also its stem is far less furrowed.

oh, yes, it is either celery or celeriac. i was just hoping that it has a big root already, but i didn't see anything big under the soil.

It is pushing up a flower stem. Like most root vegetables, once it has done that it won't develop any further underground. Clearly the growing conditions were not right and it bolted in an attempt to reproduce asap. Failure to produce a bulb is not necessarily anything to do with the quality of the seed. As I said, Celeriac is quite hard to get right. It needs space, masses of moisture, a long season and rich soil.