Is there a difference between these device terms?
Electrical engineering (and most types of engineering really) don't have a big book of 'ye old definitions'. Not only do different people use different definitions, sometimes definition will change based on context. 

For an automated-test designer, a digitizer will probably be a device that takes an analog waveform and turns it into a digital stream of bits. (the key that separates them from oscilloscopes is that they are usually continuous, instead of triggered-bursts which is what scopes do). This would be similar to what you show from the Keysight page.

For people doing something like structural analysis of a mechanical structure, a digitizer might include a bunch of sensors too. 

For an artist, a digitizer is a device that allows them to scan images or books into a digital format. 

This is also why books in the field of engineering will generally clearly define important terms so there is no confusion about them.