I was having dinner at a restaurant when Tony Steele came in

I was having dinner at a restaurant when Tony Steele came in.
这句是时间状语从句吗?一句话好好的中间突然出现when补充句子除了定语从句就状语从句了吧?不过后面那句修饰什么?感觉跟was没什么关系啊.
请问when后面的句子修饰什么？