The line 1234567 means that some people don't say lines or recite them when acting, but only say 1234567 instead, and then dub them.

In fact, this is something that has been circulating in the entertainment industry for a long time. That is to say, some actors don't recite their lines when acting, but only rely on 1234567 to participate, and only use dubbing in the later stage. The most famous one is a satirical picture of Bo Huang's impromptu guest appearance in Xiaogang Feng's "Going South". Bo Huang made a guest appearance as Mr. Digital, with no lines. 126.

So saying lines 1234567 means that some people don't say lines or recite lines when they are acting, but only say lines 1234567 instead, and then dub them later.