But instead of restoring same wallet I somehow created new one (legacy one) using this seed not understanding that it's not the same wallet? So I took one of the address and transferred btc to it.
Any electrum's seed phrase always generates same addresses. It's not possible that you import the same seed phrase and electrum generates different addresses.
Maybe, you created a new wallet instead of importing that seed phrase when you were trying to test how electrum works.
The problem with Electrum (it's probably not a problem but consequence of how seed recovering work) is that when you use anything that is accepted as seed it always creates "some" wallet. So it's easy to "restore" different wallet by mistake especially when it has no transactions on it yet.
It's not that anything is accepted as a seed phrase.
You can test this yourself. Change a word. You will see that the seed phrase becomes invalid and electrum won't allow you to generate a wallet.
Evevn if you import a BIP39 seed phrase and change a word, you will see a warning saying the checksum is failed.
Any ideas? the puzzling thing here is that seed seems like segwit but receiving address is legacy.
As said, you are using a wrong seed phrase.
Are you sure that you have never used any wallet other than electrum?
You didn't answer the question asked by o_e_l_e_o.
Do you remeber seeing any balance in your wallet?