... because Minato wouldn't known any low-class sealing jutsus used by the fodder ninja in the manga ...
... and wouldn't happen to have any sealing tags with him ...
The man's not an idiot - I'm sure he'd find out real fast that Edo's can't be killed - then he would either use a sealing jutsu on him, or, provided he doesn't know any (which is ridiculous but whatever), he would retreat and grab some sealing tags.
When he returns, Deidara will grab some clay to make bombs, and get sealed far before he's finished rummaging in his bag.
Alright, I'll stop bumping this thread now xd
speculation, speculation and more speculation , we can sit here all day and speculate, and hey he most likely did know more
but what was stated in the manga, What minato used, thats all we know