Firstly, well done for writing what you did! I wouldn’t worry too much about it being different to what Chris wrote because often programmers will quite write something just to get things working, then they’ll rewrite (refactor) their code to make it better. That could be to make it shorter, or to reorganise or split it up into multiple methods to make it easier to maintain and re-use etc. The thing to note is that this is completely normal - what you end up with is often quite different to your first attempt 
Ok let’s have a look at Chris’s code:
puts 'HEY THERE, SONNY! GIVE GRANDMA A KISS!'
while true
users_input = gets.chomp
if users_input == "BYE"
puts 'BYE SWEETIE!'
break
end
if users_input != users_input.upcase
puts 'HUH?! SPEAK UP, SONNY!'
else
random_year = 1930 + rand(21)
puts 'NO, NOT SINCE ' + random_year.to_s + '!'
end
end
I have changed it very slightly - I changed the name of the said variable, to users_input.
The program starts by printing “HEY THERE, SONNY! GIVE GRANDMA A KISS!” and then waits for user input with the gets.chomp command. By prefixing it with users_input = means the result of it will be bound to the users_input variable - which means you can then use/do something with the result.
Which is exactly what you do with the code below it; if users_input == "BYE" this is what you’ll use to terminate the program, so it needs to be assessed before anything else. If the user’s input is ‘BYE’ the program terminates by first saying “BYE SWEETIE!” then break.
If the user’s input isn’t “BYE” then that bit of code is ignored and the program moves on to the next bit of code: if users_input != users_input.upcase and what that’s doing is asking the computer to check whether the user’s input is in capital letters, which is what upcase is used for. The != bit means ‘does not’ so that full line of code is saying: let’s compare the user’s input to what we want it to to be - the user’s input in capitol letters, so for example if the user’s input was “please give me a kiss” and what we wanted was “PLEASE GIVE ME A KISS” then they would not be equal, making the if users_input != users_input.upcase statement true, which would then execute the code in that block, which is puts 'HUH?! SPEAK UP, SONNY!'.
The final part of the code will run if the user’s input is in capital letters, and in that case the program will first create a random year by choosing a random number from 0 to 21 with the rand(21) function and assign that year to the random_year variable, and then print “NO, NOT SINCE” along with the random_year converted to a string with the to_s method (followed by an exclamation mark).
Does that make sense? If so here’s what I recommend you do - change it! Alter the code to do something a little bit different. When you start doing that it will make even more sense!
Btw, I’ve split this into a dedicated thread as it could help someone else stuck on the same exercise 