Joined Twitter in 2009 (date when BTC was created)
Many people joined Twitter in 2009 on that date, not only Jeff Garzik.
Purchased the bitcointalk domain name in 2011.
theymos posted about this fact.
The forum was originally located at bitcoin.org/smf, then forum.bitcoin.org (hence the redirect), and finally bitcointalk.org. Fun fact: The name "bitcointalk" was invented by Jeff Garzik, and he's the one who bought the domain.
Who better than him to seriously create bitcoin?
But this is not enough to say Jeff Garzik is Satoshi Nakamoto and created Bitcoin. You need more evidence to conclude Jeff is Satoshi.
Satoshi created both bitcoin.org and this forum, which was originally at bitcoin.org/smf. Later, the forum got its own domain name, but due to this history, bitcoin.org and bitcointalk.org have traditionally been linked, and for quite some time Cøbra and I have together managed the domain names. However, Cøbra has never had much involvement in bitcointalk.org's operation, and I haven't involved myself in bitcoin.org for a couple of years, so the linkage between the two no longer really made made any sense.
If it is as simple as you thought, Cøbra can be Satoshi Nakamoto too.