Rabolisk is right, these are two separate ideas.
Colligative properties pertain the number of particles in solution and thus we'd expect to see an increase in BP with increasing molality. note that we're adding particles to a solution and noting a change in physical properties as a result of the "impurities". more particles will result in a increase in BP/MP deviation. this is why .02 moles of NaCl will have a larger BP elevation than .02 moles of glucose--the reason being that NaCl dissociates into two ions while glucose does not
With your ochem example, we're dealing with MW and intermolecular forces (namely van der Waals forces)--geometry can be brought into the equation if we have an example pertaining to branching. in this example however, we're dealing a pure sample of methane and octane and thus not dealing with deviations in BP/MP by adding these alkanes to an existing solution. we're simply noting how the chemical properties of each molecule affect its MP/BP
methane is much lighter and has negligible intermolecular forces and this is why it's a gas at room temperature. on the other hand, n-octane is much heavier (and linear) and can interact with others in solution via van der Waals forces and this is why it's mainly a liquid at room temperature.
