The gmail app opens your webpage through a "webview"... think of this as the equivalent as opening your website in an iframe.
The Analytics will still fire, but you won't know if was from the gmail app webview....
Some apps (gmail may be one of them.. but not sure) append a custom value to the end of their user agent strings.. usually this looks something like (including the square brackets): [somevalue]
The user agent in Adobe will still just show as whatever browser is that user's default.. likely Chrome, as the default browser is used in the webview to render the content.
If the gmail app does have this customized value, then you can create some custom code (or use Processing Rules) to look for this appended value and add some custom code to indicate "gmail app", or "facebook app" or any other apps that provide this extra data that you can leverage to identify that it was loaded via an app.
There may be other code to generically detect the use of a "webview" but I don't have that handy.