help. someone rooted or did something to phone i just bought

I just bought a SM-G900T here in iowa where I live
this is an "I-Wireless" phone which must have something to do with T-Mobile as I see some T-Mobile stuff in there like the wifi handoff

anyhow someone either tried to root it or install a rom or something
when I hold vol-down + power + home button I get to the "ODIN MODE" screen and here is what it shows:
Product Name: SM-G900T
Current Binary: Custom
System Status: Custom
Know Warranty Void: 0x1 (2)
qualcomm secure boot: enable (csb)
AP SWREV: S1, T1, R1, A1 and P1
UDC START

in settings
Galaxy S5
SM-G900T
Android 4.4.2
G900TUBU1ANCH
kerner version = 3.4.0-964333 (dpi@swdd5018 #1)
build number = NCE-G900T-4.4.2-IWI-061014-1.0.3
MDF v1.0 Release 2
VPN v1.4 Release 1

and of course Device Status = Custom

where should I go from here?
should I just try and flash a tmboile android 5.1.1 official rom over this or will there be a problem since it says custom?
thanks