PS CS5 is compatible with ACR 6.x which is the equivalent of LR 3.x. You cannot update PS CS5 to a later version of ACR
If you are using LR 4.x it is the equivalent of ACR 7.x and LR 5.x is the equivalent of ACR 8.x, so if you are using either of these Lightroom versions then you will get the warning dialog.
If you use the option "render using LIghtroom" this will ensure 100% of your Lightroom edits will be applied, if you choose "open anyway" then the older version of ACR in PS CS5 may not apply all your LR edits.