Most items have a set number -- before the Scout update introduced the Sandman, no item went higher than level 10.
About the time of the Spy / Sniper update, there was a glitch in the random drop system, and normal weapons (that usually have a fixed level number) were generated with a random level between one and one hundred. This has since been fixed, so if you see, to use one of my own items for example, a level 56 Dead Ringer, that means the item is very old. (And now with the latest patch, you'll never see a non-vintage oddly leveled item)
On the other hand, hats will always have a random level. This means nothing, but certain levels are certainly more valuable for trading, for pure sentimental value. (1, 100, 69, 42, etc.)
The singular exception to all of the above is the new Dueling Badge medal misc item, which actually "levels up" as you kill folks during your duels. A level 100 dueling badge works out to 1000 kills (Might be off a factor of ten) during duels, and likewise the rarity of the badge itself (bronze, silver, gold, platinum) is based on level increment. 0-25,26-50,51-75,76-99,100, etc.
In no case does the level of an item have any effect on gameplay.
Turn to look at your Medic and pay attention to the healing beam. If you see yellow streaks on the beam, and you see glowing yellow lights on the gun itself (without custom skins), it's a Kritzkrieg. If the Medic's backpack appears different than usual, and you see yellow and blue/green streaks on the beam, it's a Quick-Fix.
You can also watch the Medic's charge rate. If it's going up pretty quickly, chances are it's a Kritzkrieg or Quick-Fix. After a while of observing and comparing charge rates for all the mediguns, you'll be able to tell the difference at a glance.
Best Answer
Technically, they can take your name whenever they want. Your name in Team Fortress 2 is equal to your Steam profile name, and there's never been any restriction on how many people can share a single Steam name. My own name is a common English word and I share it with dozens of other profiles.
In short, you have nothing to worry about.