Update strings on testing page. (#1982)

Closes #1981

Co-authored-by: Brian Grinstead <briangrinstead@gmail.com>

ui/changes/src/testing.html

@@ -49,8 +49,8 @@
           <h3>Backed Out Commits</h3>
         </summary>
         <div class="arewe-update arewe-update-warn">
-          Note that this includes _all_ commits in a bug that gets backed out,
-          so if there are a stack of commits this can overestimate tags.
+          Note that many times _all_ commits in a bug get backed out at once, so if there are a stack of commits this can overestimate tags.
+          For instance, a commit might have been appropriately marked as `unchanged` but still get backed out.
         </div>
         <div id="backedout-chart" class="chart-container">
           <div class="chart"></div>
@@ -64,8 +64,8 @@
           <h3>Commits that caused a regression</h3>
         </summary>
         <div class="arewe-update arewe-update-warn">
-          Note that this includes _all_ commits in a bug that gets backed out,
-          so if there are a stack of commits this can overestimate tags.
+          Note that this will include _all_ commits in a bug that caused a regression, so if there are a stack of commits this can overestimate tags.
+          For instance, a commit might have been appropriately marked as `unchanged` but still be marked as causing a regression.
         </div>
         <div id="regression-chart" class="chart-container">
           <div class="chart"></div>