Sounds like an overly easy explanation, doesn't it? A Google Forms survey on vacation habits, even with 78 responses, does not justify the direct claim about identity document verification.
This link seems more vague than what is presented to us, as if all roads lead to Rome just because we saw someone walking.
The fact that 75% of travelers verify their documents in advance is just an observation, not an explanation of planning habits derived from the general survey.
For this link to be solid, the survey should have asked specific questions about the motivations behind these verifications, such as fear of administrative delays that can be long to get a cita previa appointment in Spain.
Otherwise, it's just an intuitive motif lacking concrete evidence to confirm it.