Problem building a feature vector
Analyse this code

for value in data['instructions'].iteritems(): # Here we iter by line int the instruction colunm
    myList = list(value[1]); # Here you get 1 of the values and assing to your list

myList

opcodes = [instruction.split()[0] for instruction in myList]

len(opcodes)


your "myList" variable only holds 1 of the lines (the last one) of your data, which is probably the number of instructions in that line of your dataframe

While the 30k (I don't know how panda works here) is probably the number of lines in that column (or very unlikely the sum of all instructions in every line)