Blood Pressure measurement is not static it needs to be measured over time .A 80 year old dropping blood pressure from 130/90 lying when well to 90/60 with fever and cough increased respiratory rate well above basal rate and altered mentally has very likely poor perfusion .
Capillary refill also needs measure from basal to when sick and can be dicey with age (dry thin skin)Peripheral vascular disease .
You make an excellent point that should be strongly emphasized here. Absolutely agree that closely watching the trend in your patient's numbers is FAR more useful that a single set of measurements, especially if you have any baseline information about the patient to further help you put the data in context. Reassessment, reassessment, and more reassessment.
What you do matters.