Has anyone else noticed a large spike in gmail opens this month?

Had our best performance ever this month with our regular montly eNewsletter. Looking at the email client analytics, opens from Gmail almost tripled. The only thing I can think of that would cause such a jump is the email appearing on the primary tab for everyone - is that possible? No major changes were made to template, type of content, etc.

Any ideas or thoughts are appreciated!

Thanks,
John