Why might a moving map Android app consistently record altitude off by 120 feet? I fly Cessna 172 and Cherokee Warrior both older models without a GPS.
I have a very useful freeware navigation app on my android phone which is really good in every regard other than it always reads my altitude a bit higher than were I am. 

Best example is when I am taxiing my track and its projection on the ground which should have merged are separate. 
The app does not have any setting for adjusting this! I wonder if there is any explanation for this. The app superimposes my 3d coordinates on a moving sectional chart. I re-installed the app which didn't help.
Here is my flight KML on Google Earth on my approach and landing to Catalina airport last Sunday.
While I think it would be unusual in 2016, it is possible that the unit is recording altitude as distance from the ellipsoid rather that distance from geoid (model of MSL on the earth used by the receiver).

If you use this NOAA calculator, you can find the geoid height for a single spot.  At the location you show, it's 37m or 122feet.  That's suspiciously close to the difference you're seeing.  

Output from GEOID03
                                         latitude        longitude       N 
Station Name                            ddd mm ss.sssss ddd mm ss.sssss  meters
USER LOCATION                            33 24 15.77000 119 24 57.49000  -37.259


If this error is constant over time (multiple recordings), then I think it's more plausible than random error sources.