Could this also mean Syrian?
Not necessarily. This is just a part of a sentence that one could use in many context, like "I came back from Syria" = "رجعتُ مِن سوريا"
"Syrian" is سوري .
Syria = سِریا isn't correct?
Unfortunately no, the letter "waw' is needed in the word.
In Arabic Syria= سوريا
A couple of other countries like India هند Tunisia تونس have differences while comparing with English
Like India is Hindustan in Hindi. Syria is سوريا in arabic.
Benim oğlum asker