I agree. If the head/SLT simply pop their head in your lesson, ask how it's going, ask if there are any problems and then disappear again, that's fine. But if they come in observe for 20 minutes (which is what Ofsted do) and then give you a grading, THAT'S an observation. There's a difference between checking things out in a supportive way ("I noticed that Johnny was outside your room today, what can we do to support with him and his behaviour?") and using the 20 minute observation as a stick to beat staff with (keeping staff on tenter hooks for weeks, insisting on full lesson plans throughout, assessing against Ofsted criteria in addition to performance management). A learning walk is an unobtrusive walk around the school watching what's going on but not intervening or making one's presence felt in an 'observing' fashion.