Question

but he is now working at a bank. Tony saw me and came and sa

Answer 1

跟“at”没有关系,at a bank 是泛指,并未指定哪个银行,而后者at the same table 实际上是at the same table with me,特指我就座的桌子,相当于“Tony saw me and came and sat at the table which I sat at”