As a professional inspector of runways myself, my opinion is that the Ryanair Captain did well.
A runway surface is not homogeneous. Along a single runway, the roughness and ruts (think standing water), gradient (drainage), and even the surfacing type (age, texture) varies.
The measurement of runway contamination/friction is not consistent. It can visual, or by machine. The machine can be accurate or not, it can be in-calibration or not, it can be valid for the conditions or invalid (think contamination depth vs machine calibration depth).
The reporting of runway surfacing condition is not consistent. It can be the average condition, or some statistical treatment such as the worst third, or some commercial practice such as the most optimistic.
The deposition of contamination is not homogeneous. Parts of the runway can be affected by microclimate activity (bursts of rain).
The reporting of contamination is not uniform, nor always to be trusted (loss of face, ignorance, indolence, avarice). The first world is as guilty as the third.
In practice, the system works reasonably. The addition of pilot BA reports is a worthwhile and significant input, where available from a flightdeck with a crew culture that doesn’t worry about loss of face.
For an operation in marginal conditions, where runway contamination is going to be an important factor, and the runway condition is not clearly evident, a visual inspection of the runway is commendable. IMHO the flight crew can make useful and pertinent observation from such an inspection. And IMHO as much or more so than ATC can.
The inspection of the runway is done by vehicle in the interests of safety (visibility, weather protection), communication (radio), and speed (minimum runway occupancy). I would recommend driving the full length of the runway at the carefully chosen speeds of 60 kph, returning at 100 kph. Stop in the first and again in the last third of the runway, and at each stop get out of the vehicle and “kick the dirt”, as the colloquial expression is.